In Situ Debromination-Induced Cross-Linking of Thermally Rearranged Polybenzoxazole Membranes for Enhanced Anti-CO ₂ Plasticization

Thermally rearranged (TR) polymers have emerged as promising candidates for gas separation membranes but often suffer from poor resistance to CO2-induced plasticization. In this study, rigid biphenyl (TMB) units were introduced into the polyimide backbone, and bromine atoms were incorporated into the polymer side chains to enable controlled cross-linking. The polymers underwent in situ debromination during thermal rearrangement, transforming into cross-linked PBO networks to enhance both permeability and selectivity. The optimized 50%-Br-6FTA-PBO(1:1) membrane exceeded the 2008 Robeson upper bounds for CO2/CH4 and H2/CH4 separations, as well as the 2018 upper bound for CO2/CH4 mixed gas separation. Moreover, the cross-linked network structure conferred excellent antiplasticization performance under CO2 pressures up to 600 psi and maintained stable gas separation properties over 1000 h of aging. This work provides a universal strategy for designing TR membranes that possess high permeability, high selectivity, excellent anti-CO2 plasticization performance, and long-term stability.